04Tools & Reference
The numbers and checklists you use on the job.
PT charts, unit conversions, formulas and checklists — quick reference for the workshop and the van.
Pressure / Temperature Chart
| Temp (°C) | -30 | -20 | -10 | 0 | 10 | 20 | 30 |
|---|---|---|---|---|---|---|---|
| Pressure (psig) | 6 | 17 | 28 | 41 | 56 | 73 | 92 |
Approximate reference only — always verify with the manufacturer's PT chart.
Temperature
Pressure
Formulas
Superheat
Suction line temp − saturation temp at suction pressure
Tells you if the evaporator is fed correctly. Too high = starved, too low/zero = floodback risk.
Subcooling
Condensing temp − liquid line temp
Tells you about charge and liquid-line restriction. High = overcharge/restriction, low = undercharge.
COP
Cooling capacity ÷ power input
Efficiency. Higher = more cooling per kW consumed.
Checklists
Commissioning
- 01Confirm clean system, correct components, and tightness test passed
- 02Evacuate to below 500 microns / hold
- 03Weigh in the correct charge to nameplate
- 04Start and check suction, head, superheat, subcooling
- 05Verify defrost cycle and drain
- 06Record all readings on the commissioning sheet
Service call
- 01Listen to the customer — what, when, since when
- 02Note box temp, setpoint, ambient
- 03Gauges on — suction and discharge pressure
- 04Measure superheat and subcooling
- 05Check electrical: contactor, caps, amps, controls
- 06Check airflow: coil, fans, filters
- 07Report findings and quote the fix
Fault finding
- 01Define the symptom before touching anything
- 02Get the full picture: pressures, temps, amps
- 03Form a hypothesis from the readings
- 04Test the most likely cause first
- 05Don't change parts to guess — prove the fault
- 06Repair, then re-check readings are back in range